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Community and Q&A

IAQ without central forced air

MarkFromWA | Posted in Mechanicals on

I bought a 3700 sq ft house in N. Central WA (zone 6B) with in-floor hydronic heat, and I’ve added a mini split primarily for cooling. I’ll likely switch the hydronic to a heat pump (for radiant cooling as well, to take advantage of our arid summers), and that should solve temperature.

Air quality is another story. It’s a mid-90s house, custom built with seemingly a decent attention to detail, but it’s still pretty leaky by modern standards. Guestimating based on a few factors (including the N-factor), perhaps we’re getting 100 CFM of infiltration on average.

We noticed how dusty things can get (not helped by a dry, dusty outside) and we’re in an area with significant wildfire smoke many summers, so we have a plug-in air filter for the main room and have box fan air filters when it’s really smoky outside, but we’d like to do better at filtering air and we’d like a humidifier (we’re under 30% most of winter, occasionally under 20%). But I’d also prefer not to tear down to studs.

The one arrow in the quiver is the HRV system. It has 4 returns (3 bathrooms + kitchen, each with their own wall-mounted 30-minute twist switch) and 4 supplies into common areas. The ducting is 6 inch into the HRV, and reduces down to 4 inches for the branches. Given our climate, I want to replace the HRV (lifebreath 150MAX) with an ERV, and something like the AirKing AKEV160 is appealing for it’s recirculation mode (and recirculation is overriden in favor of exhaust by the wall switches when needed). If we put in a MERV filter box and a humidifier to the supply side, I’m hoping that would do a lot to provide basic filtering and humidity. Is that at all part of a realistic solution?

But I don’t think I’ll get more than perhaps 150 CFM through those ducts, and that won’t keep up with infiltration on a windy day. So how do I solve bulk air filtering? I don’t like the plug-in air filters (they’re ugly, take up floor space, don’t move much air, use proprietary filter sizes). Each of the 3 floors has a main open area, and I have a space in mind on each floor where I could steal the top of a closet to move air from the wall on one side of the closet to the other. Is it possible to construct a built-in self-contained bulk air filter without causing a racket?

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  1. brian_wiley | | #1

    I’ll give this one a little bit of a bump and to ask if you’re measuring your indoor air quality currently. If so, can you share any data there?

  2. MarkFromWA | | #2

    We haven't been measuring IAQ. The main problem we're worried about is wildfire smoke, so we'll probably get a monitor before the summer.

  3. Izzza | | #3

    I will leave it to the experts to provide advice, but maybe you want to check out the AirThings IAQ monitors:

    Your situation sounds tricky. From the minimum amount I know, it might be hard to get proper filtration on the ERV because of the low CFM. I was shocked when I learned how restrictive MERV-16 is compared to MERV-13, for instance. I think you want MERV-16 with wildfire smoke if you are in a high-risk area.

    If you can’t get adequate filtration without some ridiculous intervention and changes to your home, maybe you could use freestanding options? IQ Air makes the best from what I’ve read. Here is an option:

    There was a time I thought I could install their whole-home system, a time before budget reality… But at least putting something like that in your bedrooms at night will be better for your health if there is wildfire smoke risk.

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